[R] Date

[Spencer Graves]

	  My speculation is that Microsoft Excel recognized that as a date and 
saved it in the "mm/dd/YYYY" format you saw when reading it into R with 
dat=read.csv("myfile.csv").


	  "str" told you the format.  You can convert that from character to 
Date using as.Date(dat$mydate, '%m/%d/%Y'), as documented in 
help('as.Date').


NOTE: The error message, "character string is not in a standard 
unambiguous format" is almost appropriate:  In this case, it's clear 
that "09/16/2019" refers to month 09, day 16, and year 2019.  However, 
if it were "09/06/2019", we would not know if it were September 6 or 9 
June of 2019.  If it were  "09/06/08", we would have the added 
possibility with the year first, followed by month and day:  June 8, 
2009.  This ambiguity is resolved most forcefully by ISO 8601.


	  Hope this helps.
	  Spencer Graves


On 11/4/21 5:30 PM, PIKAL Petr wrote:
> Hi
> 
> Not sure why the date format was changed but if I am correct R do not read dates as dates but as character vector. You need to transfer such columns to dates by asDate. The error is probably from your use two asDate commands.
> 
> Cheers
> Petr
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Val
> Sent: Thursday, November 4, 2021 10:43 PM
> To: r-help using R-project.org (r-help using r-project.org) <r-help using r-project.org>
> Subject: [R] Date
> 
> IHi All, l,
> 
> I am  reading a csv file  and one of the columns is named as  "mydate"
>   with this form, 2019-09-16.
> 
> I am reading this file as
> 
> dat=read.csv("myfile.csv")
>       the structure of the data looks like as follow
> 
> str(dat)
> mydate : chr  "09/16/2019" "02/21/2021" "02/22/2021" "10/11/2017" ...
> 
> Please note the format  has  changed from YYYY-mm-dd  to mm/dd/YYYY
> When I tried to change this   as a Date using
> 
> as.Date(as.Date(mydate,     format="%m/%d/%Y" )
> I am getting this error message
>      Error in charToDate(x) :
>        characte string is not in a standard unambiguous format
> 
> My question is,
> 1. how can I read the file as it is (i.e., without changing the date format) ?
> 2. why does R change the date format?
> 
> Thank you,
> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> Osobní údaje: Informace o zpracování a ochraně osobních údajů obchodních partnerů PRECHEZA a.s. jsou zveřejněny na: https://www.precheza.cz/zasady-ochrany-osobnich-udaju/ | Information about processing and protection of business partner’s personal data are available on website: https://www.precheza.cz/en/personal-data-protection-principles/
> Důvěrnost: Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a podléhají tomuto právně závaznému prohláąení o vyloučení odpovědnosti: https://www.precheza.cz/01-dovetek/ | This email and any documents attached to it may be confidential and are subject to the legally binding disclaimer: https://www.precheza.cz/en/01-disclaimer/
> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>